Engineering lesson
Preparing production data before a decline study
Prepare production data by preserving dates, volumes, active days and operating events. A missing value, a shut-in and a measured zero are different observations and should not be silently treated alike.
By PetroCalcHub Team · Updated October 24, 2026 · Free to read and use
Recover rate from the intended denominator
A monthly volume divided by calendar days gives calendar-average rate. Dividing by producing days gives an on-stream rate. The two answer different questions and differ when uptime changes.
The synthetic table fixes volume while changing active days to show the denominator effect. It is an accounting illustration, not a fitted decline dataset.
Retain provenance while cleaning
Keep raw rows, unit conversions, allocation changes and exclusions in a separate record. A cleaned series should be reproducible from those decisions.
A workover, constraint change or new completion can create a rate break that one smooth decline curve should not automatically absorb into b or Di.
Choose the fitting interval deliberately
Remove or model events according to a stated rule, then inspect the effect on parameters and held-out prediction. Filtering until a curve looks smooth can erase the behavior the study needs to explain.
The site's forecast workflow evaluates supplied decline parameters; it does not automatically clean production histories or fit a curve to uploaded monthly data.
Explore the example
Original synthetic teaching calculation. Equations and fixed controls are stated here; these are not field measurements.
Select one of 5 recorded scenarios. Intermediate states are not interpolated.
Active days = 15. Calendar rate (STB/day): 500; On-stream rate (STB/active day): 1000.
- Calendar rate (STB/day)
Worked example
Calendar versus producing-day rate
A 30-day month contains 15,000 STB of allocated production. Only the number of active days changes.
Relation and unit basis
calendar rate = volume/30; on-stream rate = volume/active days
The two rates use different denominators. No production-history cleaning or parameter fitting occurs in this calculation.
1. Define the baseline
Active days = 15
A 30-day month contains 15,000 STB of allocated production. Only the number of active days changes.
2. Select the relation
calendar rate = volume/30; on-stream rate = volume/active days
The two rates use different denominators. No production-history cleaning or parameter fitting occurs in this calculation.
3. Substitute the values
15,000/30 = 500 STB/calendar day; 15,000/15 = 1,000 STB/active day
Retain intermediate precision. The displayed values are rounded only after evaluation.
4. Read the result
Calendar rate (STB/day) = 500; On-stream rate (STB/active day) = 1000
Uptime changes the on-stream interpretation without changing the month's allocated volume.
Result and interpretation
Calendar rate (STB/day) = 500; On-stream rate (STB/active day) = 1000
Uptime changes the on-stream interpretation without changing the month's allocated volume.
Compare calendar-average and on-stream rates for the same volume. The forecast tool does not perform this preprocessing for you.
Exact scenario data
Original synthetic teaching calculation. Equations and fixed controls are stated here; these are not field measurements.
| Active days | Calendar rate (STB/day) | On-stream rate (STB/active day) |
|---|---|---|
| 10 | 500 | 1,500 |
| 15 | 500 | 1,000 |
| 20 | 500 | 750 |
| 25 | 500 | 600 |
| 30 | 500 | 500 |
Scroll the table to see all columns. The highlighted row is the worked baseline. Downloads retain full numerical precision.
Test your understanding
Work through the question before revealing its answer. Use the stated assumptions and include units in every numerical step.
1. A 30-day month produced 15,000 STB in 15 active days. What are the two rates?
Show the worked answer
Calendar average = 500 STB/day; on-stream average = 1,000 STB/producing day. Label the denominator.
2. Reproduce the baseline Calendar rate (STB/day) without rounding intermediate values.
Show the worked answer
15,000/30 = 500 STB/calendar day; 15,000/15 = 1,000 STB/active day. Calendar rate (STB/day) = 500. Uptime changes the on-stream interpretation without changing the month's allocated volume.
3. Compare the first and last recorded scenarios. Which input changes?
Show the worked answer
Active days changes from 10 to 30. Other controls remain as stated in the premise. Calendar rate (STB/day) changes from 500 to 500.
4. What would be needed to apply this example to a different physical system?
Show the worked answer
Replace the synthetic controls with compatible documented inputs and check the relation's assumptions. The two rates use different denominators. No production-history cleaning or parameter fitting occurs in this calculation. Uptime changes the on-stream interpretation without changing the month's allocated volume.
Before using the result
- Preserve raw dates and volumes.
- Distinguish calendar and active days.
- Record events and exclusion rules.
Uptime changes the on-stream interpretation without changing the month's allocated volume.
Continue learning
Start with the broader workflow guide
Sources and method
The explanation and synthetic examples are original PetroCalcHub teaching material. The references below support the definitions and model context. They do not supply field validation for the synthetic scenarios.